This invention relates to a process for preparing olefinic aldehydes and chemical intermediates. In another aspect, the invention relates to certain chemical intermediates per se. In a further aspect, the invention relates to a process for the stereospecific synthesis of olefinic aldehydes. In yet another aspect, the invention relates to a process for the preparation of long-chain olefinic aldehydes.
The olefinic aldehydes prepared by the process of this invention have a variety of uses. One such use is for sex pheromones.
Sex pheromones have been employed in a variety of ways for control of insect populations. For example, traps baited with appropriate pheromone compounds or mixtures can be employed to monitor for the presence of particular insects in a field. In this way, most efficient use of pesticides or other conventional means of insect control can be applied.
Traps as just described can also be used on a larger scale such that all insect pests in a given area may be lured to a trap. This technique is most effective where low-level insect populations exist. Such a trap fulfills the dual functions of monitoring for the presence of insect infestation and removing essentially all insects from the infested area, so long as the treatment program commences when insect populations are low.
The most promising means of controlling insect populations with pheromones is by permeating the atmosphere with the particular pheromone compound or mixture to which the offending insect responds. With sufficiently high levels of pheromone in the air, the searching insect becomes confused in its search for a mating partner. Since the insect cannot distinguish the artificially released pheromone from that released by a potential sex partner, propagation is greatly reduced as the likelihood of a successful encounter with a mating partner is greatly reduced.
In order to successfully apply any of the above-described methods for insect population control, the pheromone compound or mixture appropriate to the target insect must be available in sufficient quantity and isomeric purity to allow economic use of pheromone technology on a large scale. Typically, prior art synthetic methods for the preparation of pheromones have involved numerous reaction steps, one or more of which suffer from inefficient conversion of starting material to product. Frequently, expensive protecting groups are employed which do not contribute to the overall structure of the final product, thus further increasing the cost of pheromone synthesis. Further, while some compounds are effective in relatively pure form for attraction or disruption, the presence of impurities or decomposition products can inhibit or destroy the ability of the pheromone compound to affect insect behavior. Thus, time consuming and costly separation techniques are frequently required to assure the production of an essentially pure, insect active pheromone composition.
Exemplary prior art methods are described by Roelofs, Hill, Baker and Carde in U.S. Pat. No. 3,917,711; K. Mori in "The Total Synthesis of Natural Products", Vol. 4, Chapter 1, John Wiley & Sons, 1981; R. Rossi in "Synthesis" (Dec. 1977) pp. 817-836 and C. A. Henrick in "Tetrahedron" 33, 1845(1977).
Roelofs et al disclose the preparation of Z-9-tetradecenal and Z-11-hexadecenal by the chromium trioxide/pyridine promoted oxidation of Z-9-tetradecenol and Z-11-hexadecenol, respectively. This method is unsatisfactory in that large quantities of chromium trioxide are required, low product yields are obtained and extensive product workup is required to obtain satisfactorily pure product. In addition, the alcohol precursors for the final oxidation step are obtained after six reaction steps from the starting materials, 8-chloro-1-octanol or 10-chloro-1-decanol, which in turn require a starting material such as octane-1,8-diol or decane-1,10-diol. Thus, many reaction steps, low yield and large quantities of reagents are required.
K. Mori describes the preparation of cis (Z) olefins by selective hydrogenation with such as Lindlar's catalyst. The use of such selective hydrogenation catalysts is typically accompanied by the use of a hydrogen acceptor such as quinoline. These systems are effective for selective hydrogenation of hydrocarbon substituted alkynes but are incompatible with such as halogen substituted alkynes.
Rossi also discloses the use of Lindlar's catalyst, optionally in the presence of quinoline, for the selective reduction of a variety of alkynyl compounds. The starting materials employed in all examples shown are ethers, esters, alcohols or acids. Such starting materials would all require one or more additional process steps to achieve the aldehyde products desired for pheromone applications, such as the oxidation disclosed by Roelofs.
Henrick details additional exotic routes devised for the stereospecific preparation of cis-olefinic compounds useful as pheromones such as Wittig Chemistry, ylide chemistry and the like. In addition, Henrick describes a variety of oxidation processes which have been employed in efforts to overcome the disadvantages of the chromium trioxide-pyridine promoted oxidation discussed above. Each method described produces sufficient levels of impurities to create a purification problem when carried out on a large scale.
It is therefore an object of this invention to provide a process for the preparation of olefinic aldehydes. It is a further object of this invention to provide in high stereoisomeric purity cis-olefinic aldehydes. It is another object of this invention to provide a simple, economical process for the preparation in high stereoisomeric purity of cis-olefinic aldehydes useful as pheromones. It is yet another object of this invention to provide a process for the preparation of acetylenic halides, acetylenic aldehydes and olefinic halides. It is another object of this invention to provide acetylenic halides, acetylenic aldehydes and olefinic halides useful as chemical intermediates.